Plastic wastes catalytic cracking

A. Corma, S. C. Cardona, and J. Gaona Plastic wastes catalytic cracking process, WO 00/66656, 2000. 

The amount of the catalyst to be added to the waste plastic for catalytic cracking is at least 5% by weight (typically 5-10% by weight). 

Resources, Conservation Recycling 23,No.3, 1998,p.l63-81 CATALYTIC PLASTICS CRACKING FOR RECOVERY OF GASOLINE-RANGE HYDROCARBONS FROM MUNICIPAL PLASTIC WASTES Buekens A G Huang H Brussels,Free University... 

Industrial Engineering Chemistry Research 36, No.ll, Nov.1997, p.4523-9 TRANSFORMATION OF SEVERAL PLASTIC WASTES INTO FUELS BY CATALYTIC CRACKING... 

The book also explores the application of various acidic catalysts, such as silica-alumina, zeolites (HY, HZSM-5, mordenite) or alkaline compounds such as zinc oxide. However, the main problem with catalytic cracking is that in the course of the cracking process all catalysts deactivate very quickly. Expensive zeolite catalysts increase the cost of waste plastics cracking process to the point where it becomes economically unacceptable since the catalyst becomes contained in coke residue and therefore cannot be recovered and regenerated. 

K. Gobin, D. Koumantaropoulos, and G. Manos, One stage catalytic cracking of plastic waste on zeolite-based catalysts. Stud. Surf. Sci Catal, 135, 4989-4994 (2001). 

Additionally, some particular catalytic cracking processes for recovering specific raw chemicals from plastic wastes can be found in the literature. This is the case of the process... 

An alternative process based on two sequential catalytic cracking stages aimed at obtaining gasoline and diesel from waste plastics or heavy oil/waste plastics mixtures is shown in Figure 3.16 [99]. The catalyst employed in the first step is made up of powder alumina, waterglass and HZSM-5 zeolite and is mixed up directly with the waste plastics in a screw reactor preferably at 600-700°C. The second catalytic step consists in a fixed... 

Figure 3.16 Scheme of a process for the direct catalytic cracking of plastic wastes in two steps [99]... 

Another approach for overcoming the problems posed by conventional cracking catalysts has been disclosed recently by Reverse et al. [101]. In this case, direct cracking is performed by using as catalyst a molten bed of pure metal or a metal mixture (mainly lead, zinc, tin) at a temperature of 460-550°C wherein the waste polymer is loaded inside the reactor at a certain depth. The authors point out that the products are indeed a result of the combination of both thermal and catalytic cracking. The catalyst composition may also include some acidic component such as metal silicates, metal carbonates and their mixtures. The process can be applied to pure and mixed polymers (PE, PET, PP, PVC), as well as to the plastic fraction of municipal solid wastes. 

Other interesting products that can be obtained from waste plastics using combined thermal and catalytic processes are alkylaromatic compounds, which possess industrial applications as automatic transmission fluids (ATF), detergents (linear alkyl benzenes, LAB), and improvers of cetane number in diesel fuels [104]. The process uses as raw material the olefins generated in a previous step of thermal and catalytic cracking, which represent a cheaper source of olefins alternative to the currently existing ones. No special details about the conditions applied for the olefin production are indicated, the emphasis being focused on the alkylation step. Alkylation catalysts comprise conventional Lewis... 

In addition to the above-mentioned catalytic processes, there are some other related technologies wherein the catalytic cracking of plastic wastes is combined with the coprocessing of other substances, mainly coal and petroleum feedstocks (lube oil, LCO, VGO) or even a solvent. Hereafter, these technologies are explained more in detail. 

Catalytic cracking and conversion of plastics wastes is currently a field of intense research and open to innovative technologies to be discovered and applied. Significant advances have been carried out in recent years, with several commercial plants being already in operation based on the use of catalytic cracking for the plastic waste conversion into valuable products. However, there is still room for further developments. In this regard, the following fields of research can be foreseen in the next years ... 

J. Nishino, M. Itoh, T. Ishinomori, N. Knbota, and Y. Uemichi, Development of a catalytic cracking process for converting waste plastics to petrochemicals, J. Mater. Cycles Waste Manag. 5, 89 (2003). 

A. R. Songip, T. Masnda, H. Kuwahara, and K. Hashimoto, Kinetic stndies for catalytic cracking of heavy oil from waste plastics over REY zeolite. Energy Fuels 8, 136 (1994). 

J. M. Arandes, I. Abajo, D. Lopez-Valerio, I. Fernandez, M. J. Azkoiti, M. Olazar, and J. Bilbao, Transformation of several plastic wastes into fuels by catalytic cracking, Ind. Eng. Chem. Res., 36, 4523 (1997). 

D. P. Serrano, J. Aguado, J. M. Escola, E. Garagorri, J. M. Rodriguez, L. Morselli, G. Palazzi, and R. Orsi, Feedstock recycling of agriculture plastic film wastes by catalytic cracking, Appl. Catal. B Env., 49, 257 (2004). 

Because of inorganic components in waste plastics, thermal, noncatalytic processes present some advantages. In order to obtain high conversion Chinese inventors [52] propose a two-step process thermal cracking in the first step in order to obtain partial cracking of waste plastics and to separate inorganic components, and in the next step catalytic cracking of the product over a fixed-bed catalyst. 

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